This invention relates to electrostatography. More particularly, this invention relates to corona generating devices for applying electrostatic charge onto a suitable surface.
In the electrostatographic process, an electrostatographic plate comprising a photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coating which may then be developed into visible form by applying a developer material, e.g., a powder, to the plate using any one of a number of development techniques generally known and used in the art. The developer material electrostatically clings to the plate in a visual pattern corresponding to the electrostatic image. Thereafter the developed image is usually transferred from the plate to a support material such as paper to which it may be fixed by any suitable means thereby forming a permanent print.
Instead of being developed by means of a powder, the electrostatic latent image may also be developed by using liquid development techniques also well known in the art.
The charging of the electrostatographic plate in preparation for the exposure step can be accomplished by means of a corona generating device whereby electrostatic charge is applied to the electrostatographic plate to raise it to a potential of approximately 500 to 600 volts. One form of corona generating device for this purpose is disclosed in U.S. Pat. No. 2,777,957 wherein a plurality of parallel wires are connected in series to a high voltage source and are supported in a conductive shield that is arranged in closely spaced relation to the surface to be charged. When the wires are energized, corona is generated along the surface of the wires and ions are caused to be deposited on the adjacent photoconductive surface. Suitable means are usually provided to effect relative movement of the surface to be charged and the corona generating device. Such a device may have a single corona wire.
One problem associated with corona generating devices is the possible breakdown of either the surfaces or the air surrounding or coming in contact with the applied high voltage in areas other than the desired corona discharge area. For example, any sharp edges or corners on conductive members of the device tend to generate sparks to adjacent surfaces or corona. This problem is lessened by insulating all electrically conductive components of the corona device and it is an object of the present design to provide such an arrangement.
It is also important that the coronode which is generally in the form of one or more fine wires stretched between mountings at opposite ends of the device be maintained in taut condition since slackness and kinks in the coronode wires will result in non-uniformity of the charge applied to the electrostatographic plate. In order to ensure that the coronode is maintained in sufficiently taut condition it has heretofore been proposed to connect the coronode wires to at least one of the end mountings by means of a compression spring. This has the desirable feature of enabling the wires to be mounted in the device under tension while reducing the possibility of the wires, which are extremely fine (generally of the order of 0.004 inch thick), being stretched beyond its elastic limit during assembly and it is an object of this invention to provide a resilient mounting for a corona generating device in which this disadvantage is alleviated.
It is also desirable in corona generating devices to provide an arrangement for easily replacing a deteriorated corona electrode with a new one. Since this replacement usually takes place at a commercial site of a machine by a service technician, ease of replacement and adjustment in a minimum amount of time is essential.